The present invention relates to a mounting structure for a vehicular interior member. More particularly, it relates to a structure of a joining portion between an opening trim, which is fitted to an opening flange formed on a vehicle body panel of a vehicular door opening portion, and an interior member.
As a structure of a joining portion between an opening trim in a vehicular door opening portion and an interior member, there has been publicly known a structure in which the edge portion of an interior member is fixed by pinching a terminal portion (insertion piece) extending from the back surface side of an edge portion of an interior member, together with an opening flange, by the opening trim (for example, see Japanese Unexamined Patent Application Publication No. 2004-306685).
FIGS. 1 and 2 show a state in which a quarter lower trim 2, which is an interior member that covers the surface on the indoor side of a vehicle body panel 1 in a quarter portion of a four-door vehicle, is mounted. The vehicle body panel 1 is formed by weldedly joining an outer panel 11, which is usually press-molded from one steel sheet, and an inner panel 12, which consists of an assembly of a plurality of panels, at a peripheral edge of a door opening part 10. To the indoor side of a lower portion of the quarter portion, a wheelhouse inner panel 13 is joined.
The quarter lower trim 2, which is formed of a resin-molded product or the like, is locked by inserting a plurality of clips, not shown, which are protrudingly provided on the back surface side of a design surface, into holes in the vehicle body panel 1, and is configured so that in an edge part 2e along the door opening part 10, as shown in FIG. 3 or 4, an insertion piece 21 extending in a U-shape from the back surface side is fixed by being pinched, together with an opening flange 10a (11a, 12a), by an opening trim 3, the opening trim 3 being fitted in a state of being lapped on the indoor side of the opening flange 10a formed by joining an outer panel flange 11a and an inner flange 12a. 
In the case in which the quarter lower trim 2 has a three-dimensional shape having a space 20, in which an air bag, a wiring for on-board equipment, and the like are accommodated, and the edge part 2e of the quarter lower trim 2 has a vertical wall surface 2d spreading in the direction separating from the opening flange 10a (the inner flange 12a) as shown in FIG. 3, a load F1 is applied to the vertical wall surface 2d by a passenger, the vertical wall surface 2d deflects and receives a force in the direction such that the insertion piece 21 comes off or is deflected.
To provide against such a load F1, a structure in which a projection part 21a is provided in a bent portion of the insertion piece 21 so as to abut against the vertical wall surface of the inner panel 12 as shown in FIG. 4 has been disclosed in Patent Document 1. Unfortunately, this structure cannot be adopted in the case in which the inner panel 12 has a flat shape having no vertical wall surface as indicated by symbol 12′ in FIG. 4.